1. Field
The present invention relates generally to remote sensing and more particularly to passively communicating remote conditions by modulated reflectivity.
2. Background
In resource recovery, it may be useful to monitor various conditions at locations remote from an observer. In particular, it may be useful to provide for monitoring conditions at or near to the bottom of a borehole that has been drilled either for exploratory or production purposes. Because such boreholes may extend several miles, it is not always practical to provide wired communications systems for such monitoring.
U.S. Pat. No. 6,766,141 (Briles et al) discloses a system for remote down-hole well telemetry. The telemetry communication is used for oil well monitoring and recording instruments located in a vicinity of a bottom of a gas or oil recovery pipe. Modulated reflectance is described for monitoring down-hole conditions.
As described in U.S. Pat. No. 6,766,141, a radio frequency (RF) generator/receiver base station communicates electrically with the pipe. The RF frequency is described as an electromagnetic radiation between 3 Hz and 30 GHz. A down-hole electronics module having a reflecting antenna receives a radiated carrier signal from the RF generator/receiver. An antenna on the electronics module can have a parabolic or other focusing shape. The radiated carrier signal is then reflected in a modulated manner, the modulation being responsive to measurements performed by the electronics module. The reflected, modulated signal is transmitted by the pipe to the surface of the well where it can be detected by the RF generator/receiver.